Columbium-base alloy



United States This invention relates to columbium-base alloys containing tungsten in combination with zirconium and/or titanium as the major alloying ingredients.

The development of rockets and missiles and advances in gas turbines necessitate the use of materials of construction under extreme conditions of temperature and operation. It is necessary under these conditions to have superior alloys which combine workability, high-temperature strength, and high-temperature oxidation resistance in an alloy.

Accordingly, it is an object of the present invention to provide an alloy which is characterized by resistance to high-temperature oxidation even at temperatures in excess of 1000 C.

It is another object of the present invention to provide an alloy which is amenable to heat treatment by conventional means and which possesses good mechanical properties.

Still another object of the present invention is to pro vide an alloy which, when exposed to an oxidizing atmosphere at elevated temperatures, forms a pellicular metal oxide which adheres firmly to the alloy and is not substantially volatilized therefrom.

Other objects will be apparent from the subsequent disclosure and appended claims.

The alloy which satisfies the objects of the present invention consists essentially of columbium in a minimum amount of at least 45 Weight percent, 6 to 50 weight percent tungsten, up to about 15 weight percent zirconium, up to about 20 weight percent titanium, said zirconium being present in a minimum amount of at least 0.25 weight percent when the titanium content of said alloy is less than one weight percent, the titanium content of said alloy being at least 1 weight percent when the zirconium content of said alloy is less than 0.25 weight percent, up to about weight percent molybdenum, up to about 5 weight percent vanadium, the sum of vanadium, plus molybdenum not exceeding 7 weight percent, up to about 5 weight percent iron, up to about 5 Weight percent nickel, up to about 5 Weight percent cobalt, the sum of said iron, nickel and cobalt not exceeding 10 weight percent, up to about 5 weight percent tantalum, up to about 10 weight percent hafnium, up to about 1 weight percent each of barium, yttrium, beryllium and the rare earth metals, the sum of said tantalum, barium, yttrium, beryllium and rare earth metals not exceeding 10 weight percent, up to 1 weight percent carbon, up to 0.75 weight percent oxygen, up to 0.5 weight percent nitrogen, the sum of said carbon, oxygen and nitrogen not exceeding 1.5 weight percent.

The higher tungsten-titanium levels such as 5 to 20 weight percent titanium and to 35 weight percent tungsten are most beneficial from the viewpoint of oxidation resistance, while tungsten and zirconium levels in the range of 0.5 to 15 weight percent zirconium and in excess of 10 weight percent tungsten are beneficial from the viewpoint of strength, the higher zirconium range being preferred in the presence of titanium. Maximum ease of fabrication results at the higher titanium levels with zirconium contents less than 10 weight percent and tungsten contents of less than 25 weight percent.

The molybdenum and vanadium provide still further improvement in oxidation resistance as do the additions atet of iron, nickel and cobalt. The tantalum, hafnium, barium, yttrium, beryllium and rare earth metals provide both improved strength and oxidation resistance. The carbon, oxygen and nitrogen are good strengthening agents.

While the foregoing alloy satisfies all the objects of the invention the more satisfactory alloys are obtained when the alloy consists essentially of a minimum of 45 weight percent columbium, 10 to 40 weight percent tungsten, up to 15 weight percent zirconium and up to 17 weight percent titanium, said zirconium being present in a minimum amount of 0.5 weight percent when the titanium content is below 3 weight percent, said titanium being present in a minimum amount of 3 weight percent when the zirconium content is less than 0.5 weight percent, up to 4 weight percent molybdenum, up to 4 weight percent vanadium, the sum of said molybdenum and vanadium not exceeding 7 weight percent, up to 5 weight percent tantalum, up to 10 weight percent hafnium, up to 0.5 weight percent of barium, yttrium, beryllium and the rare earth metals, the sum of said tantalum, hafnium, beryllium, yttrium, barium and rare earth metals not exceeding 10 weight percent, up to 3 weight percent each of iron, nickel and cobalt, the sum of said iron, nickel and cobalt not exceeding 5 weight percent, up to 1 weight percent carbon, up to 0.5 weight percent oxygen, up to 0.3 weight percent nitrogen, the sum of said carbon, oxygen and nitrogen not exceeding 1 weight percent.

Within the limits of the foregoing alloys certain compositions of particularly superior properties have been found. These include -(a) 10 to 30 weight percent tungsten, 5 to 15 weight percent titanium, 3 to 10 weight percent zirconium, the balance columbium, (b) 15 to 35 weight percent tungsten, 5 to 10 weight percent titanium, 0.5 to 3.0 weight percent zirconium, 1 to 3 weight percent in the aggregate of molybdenum and vanadium and the balance columbium, (c) 15 to 30 weight percent tungsten, 5 to 10 weight percent titanium, 0.5 to 3.0 weight percent zirconium, l to 3 weight percent in the aggregate of molybdenum and Vanadium, l to 3 weight percent iron, 0.5 to 1.5 weight percent nickel and the balance columbium and (cl) 10 to 30 weight percent tungsten, 5 to 8 weight percent titanium, 1 to 3 weight percent zirconium, the balance columbium.

The alloys of the present invention may be prepared by any number of methods, such as the conventional methods using inert operating conditions, e.g., by the consumable arc-melting technique described in US. Patent No. 2,640,860, by the non-consumable arc-melting, by

pressing and sintering of metallic powders, or by other powder metallurgical processes. Great caution should be exercised to protect the metals from the atmosphere since contamination of the alloying mass by nitrogen and oxygen, etc., destroys many of the valuable properties of the alloy. To protect the alloying materials from these atmospheric contaminants, the alloying operation should be performed under vacuum or in an inert atmosphere, such as argon or helium, or under a protective slag or under a combination of protective slag and controlled atmosphere. The final shaping of the alloy metal may be accomplished by any of several procedures, such as forging, extrusion, swaging, rolling, or machining the cast or sintered shape.

The samples used in determining the mechanical properties cited in the examples provided below were prepared in a non-consumable arc furnace similar to that described by W. Kroll in Transactions of the Electrochemical Society, volume 78, 1940, pages 35 through 47. The procedure consists of placing the component metals in a water-cooled copper crucible, shaped to retain the charge in a hearth-like depression and incorporated in a gas-tight container supplied with a tungsten electrode capable of 9E impressing an arc onto the charge. After careful evacuation of the system, the charge was melted at least four times under an argon atmosphere until a homogeneous alloy of the desired composition was obtained. In all cases but in Example IX, the ingots were then fashioned into electrodes which were consumably arc melted into a water-cooled, copper cylindrical crucible.

The oxidation resistance of the alloys was determined using 1.60 x 0.85 x 0.65 centimeter specimens cut from tungsen arc-melted buttons. The specimens were suspended in an air-tight chamber and exposed to a stream of pure, dry oxygen at 1000 C. and 1200 C. The weight of oxygen which reacts with the specimen to form a pellicular metal oxide, was continuously measured by means of Maner type balances and was automatically recorded. By this method, an accurate measure of rate of weight gain by oxidation can be obtained. The weight gain is expressed in milligrams of weight gained per square centimeter of surface exposed for at least 100 hours at the different temperatures. Any oxide which might volatilize from the specimen during the test could be detected as a condensate formed on certain cold portions of the chamber.

The mechanical properties of the selected alloy were determined on samples which had been fabricated from the ingots by various techniques including machining from the ingot, extrusion at 1600 C. followed by hotswaging at temperatures in the range of 1000 C. to 1300 C., swaging the ingot directly at 1000 C. to 1300 C., or by forging the ingot followed by hot rolling and, in certain cases, cold rolling.

Example I An alloy containing 75 percent columbium, 20 percent tungsten, and 5 percent titanium was prepared by melting the above-cited elemental metals together in the manner set forth above, and the alloy so prepared was tested for its oxidation resistance. Under these conditions, the alloys showed a 100-hour weight gain of 546 milligrams per square centimeter at 1000 C. and a 100-hour weight gain of 2166 milligrams per square centimeter at 1200 C. Unalloyed columbium shows a weight gain of 6700 milligrams per square centimeter at 1000 C. and a weight gain of 24,000 milligrams per square centimeter .at 1200 C. under identical testing conditions. No volatile oxide was detected.

Example II An alloy was prepared containing 82 percent columbium, 10 percent tungsten, and 8 percent titanium. After having been forged, hot-rolled, and subsequently coldrolled, the alloy showed yield strengths of 44,100 p.s.i. at 850 C. and 21,100 p.s.i. at 1000 C., and ultimate tensile strengths of 55,500 p.s.i. at 850 C., 33,300 p.s.i. at 1000 C., and 16,520 p.s.i. at 1200 C.

Example III Following the testing procedure used in Example I, an alloy was prepared containing 65 percent columbium, 28 percent tungsten, and 7 percent titanium. After having been impact extruded and subsequently hot swaged, the alloy showed ultimate tensile strengths of 146,000 p.s.i. at room temperature, 72,200 p.s.i. at 850 C., and 55,800 p.s.i. at 1000 C. Upon testing for oxidation resistance, this alloy showed a 100-hour weight gain of 118 milligrams per square centimeter at 1000 C. and 208 milligrams per square centimeter at 1200 C. when tested in pure oxygen. No formation of volatile oxide Was observed and the excellent oxidation resistance of this alloy was retained at 1400 C.

Elxample IV Following the procedures described in the foregoing Examples I and II, an alloy having the composition of 67 percent columbium, percent tungsten, 10 percent titanium, and 3 percent vanadium was prepared. This alloy showed a -hour weight gain at 1000" C. of 185 milligrams per square centimeter and a weight gain of 376 milligrams per square centimeter at 1200 C. No volatile oxide was detected and this composition did not suffer the formation of loose or porous oxides in the temperature range of 500 C. to 1200 C. After having been impact extruded and subsequently hot swaged, the alloy showed ultimate tensile strengths of 122,000 p.s.i. at room temperature, 60,800 p.s.i. at 850 C. and 26,800 p.s.i. at 1200 C. At 1000 C. this alloy, in the as-swaged condiiton, exhibited an ultimate tensile strength of 56,000 p.s.i. and a yield strength of 53,000 p.s.i. with 20 percent elongation. The ductility of the alloy has been promoted by vacuum annealing at 1300 C. for one-half hour; subsequent slow cooling raised the mechanical properties due to the heat treatment to 69,500 p.s.i. ultimate and 62,000 p.s.i. yield strength at 1000 C.

Example V Adopting the procedure used in Example I, an alloy was prepared containing 57 percent columbium, 30 percent tungsten, 10 percent titanium, and 3 percent vanadium. Upon testing for its oxidation resistance, the 100- hour weight gain expressed in milligrams per square centimeter was found to be 91.3 at 1000 C. and 231 at 1200 C. No volatile oxidewas detected and this composition did not suffer the formation of loose or porous oxides in the temperature range of 500 C. to 1200 C.

Example VI Adopting the procedure used in Example I, an alloy was prepared containing 65 percent columbium, 20 percent tungsten, 7 percent titanium, 3 percent vanadium, 2 percent nickel, and 3 percent iron. Upon testing for its oxidation resistance, the 100-hour weight gain expressed in milligrams per square centimeter was found to be 46.3 at 1000 C. and at 1200 C. No volatile oxide Was detected and this composition did not suffer the formation of loose or porous oxides in the temperature range of 500 C. to 1200 C.

Example VII Adopting the procedure used in Example I, an alloy was prepared containing 66.5 percent columbium, 20 percent tungsten, 10 percent titanium, 3 percent vanadium, and 0.5 percent beryllium. Upon testing for its oxidation resistance, the 100-hour weight gain expressed in milligrams per square centimeter was found to be 43.6 at 1000 C. and 304 at 1200 C. No volatile oxide was detected and this composition did not suffer the formation of loose or porous oxides in the temperature range of 500 C. to 1200 C.

Example VIII Adopting the procedures used in Example I, an alloy was prepared containing 67 percent columbium, 20 percent tungsten, 7 percent titanium, 3 percent vanadium, 1 percent nickel, and 2 percent iron. Upon testing for its oxidation resistance, the 100-hour weight gain expressed in milligrams per square centimeter was found to be 46.3 at 1000 C. and 344 at 1200 C. No volatile oxide was detected and this composition did not suffer from the formation of loose or porous oxides in the temperature range of 500 C. to 12 00 C.

Example IX Using non-consumable arc-melting, an alloy was prepared having the composition of 84.9 percent columbium, 9.4 percent tungsten, and 4.7 percent zirconium. Actual analysis of the ingot was tungsten 9.7 weight percent, zirconium 4.9 weight percent, carbon 0.03 weight percent, oxygen 0.08 weight percent, nitrogen 0.016 weight percent, and hydrogen 0.001 weight percent. Samples were machined from the ingot and subsequently annealed for one hour in vacuo at 1700 C. The alloy showed yield strengths of 71,250 p.s.i. at room temperature; 35,900

p.s.i. at 850 C.; and 29,100 p.s.i. at 1200 C., and ultimate strengths of more than 74,000 p.s.i. at room temperature; 56,000 p.s.i. at 850 C.; and more than 45,000 p.s.i. at 1200 C.

Example X Adopting the procedure used in Example I, an alloy was prepared containing percent tungsten, 10 percent titanium, 5 percent zirconium, and the balance columbium. Upon testing for its oxidation resistance, the 100-hour Weight gain expressed in milligrams per square centimeter was found to be 273 at 1000 C. and 558 at 1200 C. No volatile oxide was detected and this composition did not suffer the formation of loose or porous oxides in the temperature range of 500 C. to 1200 C.

Example XI Adopting the procedure used in Example I, an alloy was prepared containing 72 percent columbium, 10 percent tungsten, 10 percent titanium, 3 percent vanadium, and 5 percent zirconium. Upon testing for its oxidation resistance, the 100-hour weight gain expressed in milligrams per square centimeter was found to be 512 at 1200 C. No volatile oxide was detected and this composition did not suffer the formation of loose or porous oxides in the temperature range of 500 C. to 1200 C.

Example XII An alloy was prepared having the composition of 65 percent columbium, percent tungsten, 10 percent titanium, and 10 percent zirconium. After having been forged and subsequently hot-rolled, the alloy showed, at 1000 C., a yield strength of 51,600 p.s.i. and an ultimate strength of 60,900 p.s.i.

Example XIII Using consumable arc melting, an alloy was prepared having the composition 75 percent columbium, 15 percent tungsten, 5 percent titanium, and 5 percent zirconium. After extrusion and rolling to sheet at temperatures as low as 600 C., the alloy showed yield strengths of 120,000 p.s.i. at room temperature, 69,000 p.s.i. at 1000 C., and 26,000 p.s.i. at 1200 C. with ultimate tensile strengths of 131,000 p.s.i. at room temperature, 76,000 p.s.i. at 1000 C. and 32,000 p.s.i. at 1200 C. In addition, when tested for oxidation resistance, the 100- hour weight gain in pure oxygen expressed in milligrams per square centimeter was found to be 679 at 1000 C. and 554 at 1200 C.

Example XIV Adopting the procedure used in Example I, an alloy was prepared containing 67 percent columbium, percent tungsten, 10 percent titanium, and 3 percent molybdenum. The 100-hour weight gain expressed in milligrams per square centimeter was found to be 107 at 100 C. and 249 at 1200 C. No volatile oxide was detected and this composition did not suffer the formation of loose or porous oxides in the temperature range of 500 C. to 1200 C.

Although it is preferable to use high-purity metals in the preparation of the alloys of the present invention, a small amount of variance in purity can be tolerated before product quality suffers appreciably. The alloys of the working examples are prepared from commercially available metals which contain a small percentage of incidental impurities.

Certain specific compositions have been found to have exceptional properties. These compositions are shown in Table I:

TABLE L-ALLOY COMPOSITION Percent Columbium 84.9 65.0 57.0 67.0 75 67 Tungsten .4 .0 .0 20.0 15 28 Titanium .0 0 10.0 5

Vanadium .0 0 3.

Zirconium Nickel- Molybdenum What is claimed is:

1. An alloy comprising 10 to 30 weight percent tungsten, 5 to 15 weight percent titanium, 3-10 weight percent zirconium and the balance columbium and incidental impurities.

2. An alloy comprising about 5 weight percent zirconium, about 10 weight percent tungsten and the remainder columbium.

References Cited by the Examiner UNITED STATES PATENTS 2,822,268 2/1958 Hix 174 2,838,396 6/1958 Rhodin 75-174 2,883,282 4/1959 Wainer 75174 2,973,261 2/1961 Frank 75-174 FOREIGN PATENTS 1,226,436 7/1960 France.

OTHER REFERENCES Investigation of Some Niobium-Base Alloys, Battelle Memorial Institute, Oct. 31, 1956, 16 pages.

HYLAND BIZOT, Primary Examiner.

RAY K. WINDHAM, MARCUS U. LYONS, JOHN R. SPECK, WINSTON A. DOUGLAS, DAVID L. RECK, Examiners.

N. A. RAUTIOLA, W. B. NOLL, W. C. TOWNSEND,

C. N. LOVELL, Assistant Examiners. 

1. AN ALLOY COMPRISING 10 TO 30 WEIGHT PERCENT TUNGSTEN, 5 TO 15 WEIGHT PERCENT TITANIUM, 3-10 WEIGHT PERCENT ZIRCONIUM AND THE BALANCE COLUMBIUM AND INCIDENTAL IMPURTIES. 